1. Field of the Invention
The invention relates to a radio-opaque dental prosthetic member consisting of a composite material comprising longitudinal fibres such as glass fibres or quartz fibres embedded in a resin matrix.
In the rest of the description, the expression “prosthetic member” means a prefabricated composite material comprising longitudinal fibres embedded in a resin matrix for use in dentistry and in particular a dental post, an intradental post, a bridge reinforcement and preform for CAPC suitable for adhesion using a photopolymerizable or dual cement.
The invention is described more particularly in relation to dental posts made from composite material.
2. Description of the Related Art
Dental posts are used for the reconstruction of pulpless teeth. Two types of post are distinguished, respectively metal or ceramic posts, and composite posts.
Metal posts are generally made from stainless steel. They have the drawback of being subject to corrosion. Moreover, they have a different transverse elastic modulus from that of dentine, ultimately giving rise to detachment of the post.
To solve these problems, posts made from composite material have been proposed such as those described in particular in document EP-A-0 432 001 of the Applicant. These posts consist in practice of long fibres, of glass or carbon, embedded in a biocompatible thermoset resin matrix.
The essential drawback of the posts described in this document is that they are not radio-opaque to X-rays, making it difficult to locate them accurately at the time of their implant, but also in case of accidental ingestion.
To solve the problem of radio-opacity, document EP-A-0 793 474 proposes incorporating fillers based on metal oxide in the matrix, for example zirconium oxide. These fillers generally consist of micron-sized particles which effectively confer radio-opacity to the post, but which often form therewith aggregates generally having a size between 1 and 5 μm, increasing the viscosity of the resin and making its application difficult. Moreover, the volume occupied by the fillers represents a volume that is no longer available for the reinforcing fibres, commensurately decreasing the mechanical properties of the final material, mechanical properties which are nevertheless essential for the prosthetic members of the invention. Furthermore, the particles, the aggregates or their defects have comparable dimensions to the wavelengths of visible radiation. The light radiation issuing from the lamp for photopolymerization is therefore scattered when passing through the post, whose transparency to visible radiation is low. Furthermore, the non-uniform distribution of the aggregates in the post affects its aesthetic character.
Document FR-A-2 874 498 describes dental blocking members of composite material said to be transparent to light rays and comprising a matrix reinforced with fibres and containing radio-opaque particles, having a size close to a quarter of the wavelength of an incident radiation emitted by a photopolymerization lamp. In practice, the size of the radio-opaque particles is between 95 and 200 nm when the incident radiation wavelength is between 380 and 800 nm. Nothing is indicated concerning the usable types of radio-opaque particles. In fact, if for example zirconium oxide is used, a well-known radio-opaque component mentioned in document EP-A-0 793 474, having a size of about 100 nm, the incident radiation is not transmitted. Furthermore, even if the particle size is much lower than that of the metal oxides used in document EP-A-0 793 474, aggregates are still formed, and their presence in the matrix causes the same drawbacks as discussed above.
Document EP 1 227 781 A1 describes fibreless dental materials, and in particular cements and adhesives comprising a high proportion of silica nanoparticles (at least 40% by weight of the material), thereby providing a reasonably transparent material having satisfactory Theological properties in the uncrosslinked state (making the material easy to handle by the practitioner) and hard in the crosslinked state. The material may also contain radio-opaque heavy metal oxides, having a size close to 60 nm, whereof the surface is treated chemically to permit their absorption in the said material.